1. Field of the Invention.
High quality pectins are an important ingredient in many confectionary products. This invention relates to a method of extracting high quality pectin from citrus, apple and other pectin-containing plant materials by the application of high-energy microwaves under pressure.
2. Description of the Related Art.
A significant amount of research on pectins has been carried out due to its importance as a food product, a dietary fiber and a component of cell walls in higher plants, and to the growing awareness of a number of pharmacological activities. Conventional methods of pectin extraction from all the above pectin sources do not produce pectins of sufficient quality for such uses, however. As a result, millions of pounds of pectin extracted from raw materials such as orange peels are used as low-value animal feed. The high value of food quality pectins has prompted researchers to search for methods of pectin extraction which will increase the yield and the quality of the product. Currently available high-quality pectins are predominantly obtained from lime and lemon peels and are extracted by conventional methods.
By current methods, pectin is extracted from citrus peel in heated water (approximately 85.degree. C.) at acid pH (about 1-3) for a period of time in excess of 30 min. Manabe et al. (1988. Nippon Shokuhin Kogyo Gakkaishi 35. pp. 497-501) reported the use of microwave energy in an open vessel to extract pectin from mandarin orange pulp. About 5% more pectin could be extracted in 15 min than could be extracted in 60 min by conventional methods of heating at 85.degree. C. Kratchanova et al. (1994. Carbohydrate Polymers. vol. 25, pp. 141-144) reported that microwave pretreatment of crushed fruit materials increased pectin yield and resulted in a product having a higher degree of esterification and gel strength compared to conventional methods alone. In a subsequent study, Kratchanova et al. (1996. Pectins and Pectinases. Visser, J. and Voragen, A. G. J., eds. Elsevier Science, pp. 941-946) reported that increases in intensity (0.45-0.9 kW) and time (2-20 min) of microwave treatment had a favorable effect on pectin yield and quality.
Although these processes do not produce pectins which meet quality standards as high as the process described herein, the results indicated that microwave energy was potentially useful in an extraction process.